Specifications

MGE UPS SYSTEMS - Galaxy 3000 Specification 5 Effective: September, 2006
2.3 MODES OF OPERATION
The UPS module shall be designed to operate as a double conversion, on-line reverse transfer system in
the following modes.
A. Normal: The inverter shall continuously supply power to the critical load. The PFC rectifier shall derive
power from the utility AC source and supply DC power to the inverter, while simultaneously float charging
the battery.
B. Emergency: Upon failure of the utility AC power source, the critical load shall be supplied by the inverter,
which, without any interruption, shall obtain its power from the battery.
C. Recharge: Upon restoration of the utility AC power source (prior to complete battery discharge), the PFC
rectifier shall power the inverter and simultaneously recharge the battery.
D. Bypass Mode: The static bypass transfer switch shall be used to transfer the load to the bypass without
interruption to the critical power load. This shall be accomplished by turning the inverter off. Automatic re-
transfer or forward transfer of the load shall be accomplished by turning the inverter on.
E. Maintenance Bypass/Test Mode: A manual make before break internal maintenance bypass switch
shall be provided to isolate the UPS inverter output and static bypass transfer switch for maintenance.
This shall allow the UPS to be tested or repaired without affecting load operation.
2.4 COMPONENT DESCRIPTION
A. PFC Rectifier and Battery Charger
Incoming AC power shall be converted to a regulated DC output voltage by an IGBT (insulated gate
bipolar transistor) power factor corrected (PFC) rectifier. The rectifier shall provide high quality DC
power to charge the batteries and power the inverter and shall have the following characteristics:
1. Input Power Factor Correction (PFC): The PFC rectifier shall be power factor corrected so as to
maintain an input power factor of 0.98 lagging to unity at all load levels to ensure generator
compatibility and avoid reflected harmonics from disturbing loads sharing the utility power.
2. Input Harmonic Current Suppression: The PFC rectifier shall produce a sinusoidal input AC
current on each phase with low harmonic content, limiting THD on the UPS input to below 3%. This
shall eliminate the requirement for an input filter.
3. Modular Assembly: The PFC rectifier assembly shall be constructed of modular design to facilitate
rapid maintenance.
4. Battery Charger Current Limiting: The UPS shall be equipped with a system designed to limit
the battery recharge current (from 0.05 C10 to 0.1 C10).
5. Charging Levels: The ‘battery charging circuitry’ shall be capable of being set for automatic
battery recharge operation, float service, manual battery charge service, and equalizing or
commissioning operation.
6. Intermittent Charging: The battery charge level shall be maintained by an intermittent charging
technique between two values Vfmin and Vfmax very close to the floating voltage. This technique
shall be based on a cycle made up of a short charge period (a few seconds) from Vfmin to Vfmax
followed automatically by a slow discharge period (a few minutes) from Vfmax to Vfmin. This cycle
shall be repeated continuously to maintain the battery charge level. In this way the battery shall
actually be charging only for a small part of the time, which considerably increases its service life.